1. Technical Field
The present disclosure generally relates a packet scheduling method using in a broadband wireless network, and more particularly to a frame aggregation-based packet scheduling method being capable of power saving, and to a communication apparatus using the same.
2. Description of Related Art
The mobile subscriber station (abbreviated as “MSS”) has the sleep mode specified according to IEEE 802.16e standard. The sleep mode is used to reduce the power consumption of the MSS. Assuming the MSS and the base station (abbreviated as “BS”) have establish the connection, if there are no packets received or transmitted by the MSS for a certain time period, the MSS may switch from the normal mode to the sleep mode. The duration of the sleep mode can be divided into several cycles, and each cycle may also comprises both of the sleep and listen intervals. In the listen interval, the MSS can receive or transmit the data, or listen to a medium access control (abbreviated as “MAC”) message from the BS. In the listen interval, the MSS may switch to the sleep power state, or the MSS may associate with the other neighbor BSs for handover scanning purpose.
The IEEE 802.16e standard defines three types of the power saving mechanisms in the WiMax system. Referring to FIG. 1, FIG. 1 is schematic diagram showing the three types of the power saving mechanisms in the WiMax system. The detailed introduction of the three types of the power saving mechanisms in the WiMax system is stated in the following description. With respect to the first type of the power saving mechanism, the sleep interval in the sleep mode is exponentially growing. For example, when the first type of the power saving mechanism is used, the time period of the sleep mode contains the sleep intervals 101, 103, 105, and listen intervals 102, 104, 106, wherein the sleep interval 103 is the twice of the sleep interval 101, and sleep interval 105 is the twice of the sleep interval 103. With respect to the second type of the power saving mechanism, the sleep interval in the sleep mode is fixed. For example, when the second type of the power saving mechanism is used, the time period of the sleep mode contains the sleep intervals 111, 113, 115, and listen intervals 112, 114, 116, wherein the total time length of the sleep intervals 111, 113, 115 are identical. With respect to the third type of the power saving mechanism, the sleep mode does not contain any listen interval, but contains a long sleep interval. For example, when the third type of the power saving mechanism is used, the time period of the sleep mode merely contains the sleep interval 121.
The above three different types of the power saving mechanism are designed to the single connection. However, in the general case, the MSS may simultaneously have many connections, and the above power saving mechanisms can not be used to achieve the end of power saving. Assuming there are two connections of different types, and the sleep intervals of the two connections are T, if the time offset between the two sleep intervals is T/2, it results the MSS always operates in the high power consumption state, thus being unable to save power.
Referring to FIG. 2, FIG. 2 is schematic diagram showing the sleep frames and sleep frames in the sleep mode generated by the MSS having a plurality of connections. In FIG. 2, the parameter Tf represents a frame time length, the MSS and the BS have established a plurality of connection links, for example, the connections CID1-CID3. The MSS determines the listen intervals and the sleep intervals between the MSS and the BS according to the listen intervals and the sleep intervals of CID1-CID3.
Regarding the connection CID1, its delay constraint D1 is triple of the frame time length Tf, i.e. D1=3Tf. The listen interval of the connection CID1 comprises the frame periods 201, 204, 207, and 210. The sleep interval of the connection CID1 comprises the frame periods 202, 203, 205, 206, 208, and 209. During the frame periods 201, 204, 207, and 210, there are a plurality of data bursts B01-B04 generated for the connection CID1.
Regarding the connection CID2, its delay constraint D1 is triple of the frame time length Tf, i.e. D2=3Tf. The listen interval of the connection CID2 comprises the frame periods 203, 206, and 209. The sleep interval of the connection CID2 comprises the frame periods 201, 202, 204, 205, 207, 208, and 210. During the frame periods 203, 206, and 209, there are a plurality of data bursts B11-B13 generated for the connection CID2.
Regarding the connection CID3, its delay constraint D3 is four times of the frame time length Tf, i.e. D3=4Tf. The listen interval of the connection CID3 comprises the frame periods 201, 205, and 209. The sleep interval of the connection CID3 comprises the frame periods 202-204, 206-208, and 210. During the frame periods 201, 205, and 209, there are a plurality of data bursts B21-B24 generated for the connection CID3.
In the listen interval of each connection, there is a data burst generated. With respect to the MSS supporting the unsolicited grant service real connection, the data burst generated in each frame period of the connections CID1-CID3 are aggregated into the frame thereof, and the frame period is the listen interval in the sleep mode. If there are no data bursts generated in some frame period of the connections, the frame period is the sleep interval in the sleep mode.
Taking FIG. 2 as an example, the frame period 201 is the listen interval when the MSS operates in the sleep mode, wherein the frame in the frame period 201 comprises the data busts B01, B21 of the connections CID1, and CID3. The frame period 202 is the sleep interval when the MSS operates in the sleep mode, because there are no data bursts for the connections CID1-CID3 in the frame time 202. The frame periods 203-207 are the listen intervals when the MSS operates in the sleep mode, wherein the frame in the frame period 203 comprises the data burst B11 for the connection CID2, the frame in the frame period 204 comprises the data burst B02 for the connection CID1, the frame in the frame period 205 comprises the data burst B22 for the connection CID3, the frame in the frame period 206 comprises the data burst B12 for the connection CID2, and the frame in the frame period 207 comprises the data burst B03 for the connection CID1. The frame period 208 is the sleep interval when the MSS operates in the sleep mode, because there are no data bursts for the connections CID1-CID3 in the frame time 208. The frame periods 209 and 210 are the listen intervals when the MSS operates in the sleep mode, wherein the frame in the frame period 209 comprises the data burst B13 for the connection CID2 and data burst B23 for the connection CID3, and the frame in the frame period 210 comprises the data burst B04 for the connection CID1.
To solve the problem which the power saving algorithm can not be used in the case with multiple connection links, several patent applications and academic papers now have proposed a plurality of packet scheduling methods for dealing this problem. However, the packet scheduling methods consider all of the connection links to schedule.